1. Technical Field
The invention relates to inspecting a discharge state of a liquid discharging apparatus.
2. Related Art
Ink jet type printers perform printing by discharging ink inside a cavity. The ink thickens after drying. When the ink inside the cavity is thickened, there are times when this causes discharge failures. In addition, when bubbles are included in the ink inside the cavity or when paper dust is attached to the nozzles which discharge the ink, there are times when this causes discharge failures. Thus, it is preferable to inspect the discharge state of the ink.
JP-A-2004-276544 (FIG. 31) discloses a method where the discharge state is determined by applying vibration to the ink inside the cavity using a piezoelectric element and detecting the behavior of ink with respect to the residual vibration thereof.
Here, the behavior of the ink is detected according to electromotive force of the piezoelectric element. Accordingly, it is necessary to apply a driving signal for inspecting the piezoelectric element in the step where the vibration is applied to the ink and to extract the electromotive force from the piezoelectric element in the step where the residual vibration of the ink is inspected. In more detail, JP-A-2004-276544 (FIG. 31) discloses a switch which selects a driver which supplies a driving signal and a head abnormality detecting unit which detects abnormalities in a head based on electromotive force and which connects the driver and the head abnormality detecting unit with the piezoelectric element.
However, with respect to a driving signal which has a large amplitude, the electromotive force of the piezoelectric element according to the residual vibration has a small amplitude. Since the piezoelectric element has a capacitive load, the potential according to the driving signal is held by the piezoelectric element even when the supply of the driving signal is stopped. For this reason, the potential of the piezoelectric element which is supplied to the head abnormality detecting unit directly after switching from applying the driving signal to the detecting of the electromotive force is the potential of the driving signal directly before switching. Thus, there is a problem in that the dynamic range of the head abnormality detecting unit is inevitably increased and a high voltage is necessary for the power voltage which is necessary in the head abnormality detecting unit in the same manner as for the driver which outputs the driving signal.